My FIL was diagnosed with LBD about four years ago (he died threee years post diagnosis). It's a form of dementia that's closely linked with Parkinsons, so it can cause some physical as well as cognitive symptoms such as stooped posture, shuffling gait and a tendency to 'freeze'. It's often characterised less by memory loss in the early stages than by other cognitive issues, such as difficulty with executive tasks. It can be very up and down - FIL would have times in the day when he'd completely zone out, and other times when he'd be pretty 'normal'. It often comes with sleep issues (REM sleep disturbance, which is basically where people physically 'act out' dreams), sometimes years before diagnosis, and can cause loss of sense of taste and smell (FIL had both of these for years prior to diagnosis).
Another hallmark is hallucination even in the early stages - things like seeing children and animals. FIL appeared to have this less than some - but he did have times when he became confused and suspicious over who people were (thinking his children were employees, or thinking his wife was an impostor). Luckily, he was very rarely violent, but he did occasionally lash out or physically resist attempts to calm him in response to his more confused episodes (eg when he thought a family member was someone else).
I'm really, really sorry OP - it's a very difficult diagnosis. Medication did help FIL to an extent - it seemed to reduce the 'impostor' syndrome and lessen some of his distress. He lived at home for nearly three years after diagnosis, but it got harder and harder - towards the end of that time he was deeply confused a lot of the time, and spent quite a lot of the day either asleep in a chair or zoned out, or more awake but fretful, and his nights were quite disturbed. Eventually, after increasing amounts of respite care, because MIL just couldn't cope, he went into a care home permanently, but he died a couple of months later (of a stroke - no idea if related to the dementia). To be brutally honest, I think it was a blessing that he didn't have to go on for longer, as he had very little quality of life by that stage and was frequently either utterly confused or sometimes distressed.
I'm sorry that this is a negative post, but I don't want to sugar coat. What I would say above all us that it's very, very tough on a spouse to care for someone with LBD. It sounds like your DF might have been masking how bad things have been? Of course you'll want to do the best for your DM, but actually it might be your DF who is at least as much in need of support. Looking back, I don't think we really, properly appreciated how hard it was until quite late on.
My heart goes out to you - and please feel free to ask any questions. I'm no expert, but I did see this illness up pretty close and read an awful lot about it online at the time. In terms of advice, I don't have much - except to ask the medical team about drugs (if she's not already on them) and to start looking at what care might be available to help support your DF. Is your DM admitted to hospital at the moment?